Receiving system



July 7, 1936. R. A. BRADEN RECEIVING SYSTEM FiledJan. 9, 1952' 2sheets-sheet 1 Arlll IIII INVENTOR l' RENE A. BRDEN NQ M nw k w w w Mw@.Q

NSKMNNUQQ ATTORNEY July 7, 1936.

R. A. BRADEN RECEIVING SYSTEM Filed Jan. 9,1952 2 Sheets-Sheet 2 .1@WEWPatented July 7, 1936 UNH'E'ED STATES RECEIVING SYSTEM Rene A. Braden,Merchantvilie, N. J., assigner to Radio Corporation of America, acorporation of Delaware Application January 9,

11 Claims.

My present invention relates to electrical wave receiving systems, andmore particularly to novel methods of, and means for, amplifying theamplitude of the carrier wave of intelligence modulated carrier energywith respect to the side bands of such carrier energy.

In the reception of modulated carrier energy there eXist varioussituations where it is eX- tremely desirable to effect amplification ofthe carrier amplitude with respect to side band amplitude after themodulated carrier energy has been received. For example, interferencebetween broadcasting stations may be considerably reduced bybroadcasting energy from each station in such a manner that the sidebands are transmitted at full amplitude, While the carrier wave istransmitted at much reduced amplitude. It can be demonstrated that wheninterfering stations also transmit with reduced carrier in this manner,interference is effectively reduced. In order to receive such broadcastenergy it is necessary at the receiving point to amplify the carrierwave of the received energy more than the side bands so as to bring thecarrier up to normal amplitude at the detector input.

Accordingly, it may be stated that it is one of the main objects of thepresent invention to provide a meth-od of reception of modulated carrierenergy wherein the energy is transmitted with 30 the side bands at fullamplitude and the carrier at much reduced amplitude, which receptioncomprises tlie steps of selectively separating the carrier wave from theside bands, amplifying the carrier from subnormal amplitude to normalam- 35 plitude, and then combining the amplified carrier and the sidebands, both at normal amplitude, for detection and utilization.

While it has been pointed out heretofore that modulated carrier energymay be deliberately 40 transmitted with a carrier wave of sub-normalamplitude, it is also known that natural phenomena, as represented bythe action of the socalled Heavyside layer, result in reception behavioroften termed selective fading. Selec- 45 tive fading signifies theattenuation of a relatively narrow portion of the radio frequency band,this attenuation varying with time in an irregulai` manner, and alsoshifting from onefrequency range to another within the band.

When the attenuation band happens to be at the center of the transmittedfrequency band, so that the carrier is reduced in amplitude, distortionoccurs in the detection process. Especially is this so if the carrier isreduced to a small fraction of its normal amplitude. According to 1932,Serial No. 585,646

(Cl. Z50-20) my present invention it is possible to correct suchselective fading, fidelity of reproduction of short Waves beingparticularly improved.

Another important object of the present invention is to provide a novelmethod of reducing the harmful effects of selective fading, and ingeneral receiving modulated carrier energy wherein the carrier wave isreceived at subnormal amplitude, the method consisting in separating thecarrier Wave and the side bands at a relatively low radio frequency,amplifying the separated carrier and side bands independently, andsubsequently combining the carrier Wave and side bands, both atsubstantially the same amplitude for detection and utilization.

It has been pointed out heretofore that the present invention may beeffectively employed to receive modulated carrier energy in cases wherethe received energy is collected with its carrier at subnormalamplitude. In each of the cases discussed above it has been the objectof the invention to elevate the carrier amplitude from subnormal valueto a normal value.

However, the present invention can be utilized, after separation ofthecarrier wave from the side bands, for elevating the amplitude of thecarrier wave from a normal amplitude to a superno-rmal amplitude. Thisvariation of the present invention can be employed to great advantage inreducing the production of harmonics in the output of a detectorcircuit.

It is Well recognized that rectification of modulated signals producesnot only audio frequency currents of the original modulation frequency,but also second, and higher, harmonics, as well as sum and differencefrequencies. The amount of extra frequencies depends on the degree ofmodulation of the carrier wave. Hence, by reducing the effectivemodulation degree of the received carrier wave, the production ofharmonics in the output of the detector will be considerably minimized;it being emphasized that elevation of the carrier amplitude from normalto supernormal value results in reduction of the degree of modulation.

Another important object of the present invention can, therefore, besaid to reside in providing a method of separating the carrier wave ofreceived modulated carrier energy from its side bands, and treating theseparated carrier wave in such a manner with respect to the side bandsythat the degree of modulation of the received carrier wave is reducedwith the result that production of harmonics in the detector output ofthe receiver is considerably minimized.

Still another object of the present invention is to provide a method ofreceiving modulated carrier energy which consists in collectingmodulated carrier energy, separating the carrier wave from the sidebands, amplifying the separated carrier wave independently of the sidebands to a predetermined Value, combining the amplified carrier wave andthe side bands, and finally detecting the combined energies.

Still other objects of the present invention are to improve generallythe efficiency of radio reception, and to particularly provide a radioreceiver wherein the carrier of the received signal is amplified morethan the side bands thereof thus resulting in a receiver which is notonly reliable in short wave reception, but capable of reducing detectordistortion, due to harmonic production in the detector output, to agreat extent.

The novel features which I believe to be characteristic of my inventionare set forth in particularity in the appended claims, the inventionitself, however, as to both its organization and method of operationwill best be understood by reference to the following description takenin connection with the drawing in which I have indicateddiagrammatically several circuit or ganizations whereby my invention maybe carried into effect.

In the drawings,

Fig. 1 diagrammatically shows a radio receiver embodying one form of thepresent invention,

Fig. 2 diagrammatically shows another embodiment of the invention, and

Fig. 3 shows still another form of the invention in diagrammatic manner.

Referring, now, to the accompanying drawings wherein like characters ofreference indicate the same parts in the different figures, there isshown in Fig. l a radio receiver system wherein modulated carrier energyis collected, amplified and detected for utilization in any well knownmanner, numeral I designating in conventional manner a source of signalenergy, as for example an antenna system. It is to be understood thatthe energy collected at the source I is for one reason or anothercomposed of side bands transmitted at full amplitude, and a carrier waveat much reduced amplitude.

As has been hitherto stated, this reduction of carrier amplitude may bedue to a deliberate transmission technique. For the reduction ofinterference between broadcast stations the side bands may betransmitted at normal amplitude, while the carrier may be transmittedfrom each broadcast station at considerably reduced amplitudes. Themanner in which such transmission from broadcast stations is to beaccomplished is not illustrated, nor referred to in detail, except topoint out that methods are well known to those skilled in the artwhereby such transmission may be readily accomplished. To receive suchwaves at the receiver shown in Fig. 1, the carrier is amplified muchmore than the side bands, so as to bring the carrier amplitude up tonormal at the detector input. This is necessary, as will be readilyrealized, because detection of the received energy with a carrier ofsubnormal amplitude would result in serious distortion.

Accordingly, the source I is coupled to two different amplificationpaths. One of these paths comprises a multi-stage radio frequencyamplifier 2 which is adapted for tuning to the desired carrier wavefrequency. The amplifier 2 is conventionally represented, as any type ofmultiventionally disposed in its amplifier stage radio frequencyamplifier may be employed which is well known to those skilled in theart, it being understood that the amplifier 2 will include a tuningdevice 3, such as one or more variable condensers, each condenser beingdisposed in the input of each stage of amplification in the well knownmanner, the input of the amplifier 2 being coupled as at M, to thesource I. The output of the amplifier 2 is coupled, as at Mi, to thetunable input of the conventionally represented detector 4.

The tuning means of the detector input may also comprise a variablecondenser 5, the latter being connected by any mechanical control device6 for uni-control with the tuning means of the amplifier 2. The source Iis, additionally, coupled, as at M3, to a carrier wave amplifier l, theinput of which is tuned by a variable condenser 8. While the amplifier'I has been conventionally shown, it is to be understood that it maycomprise one or more stages of amplification, as in the case of theamplifier 2, and that each stage of such amplification may be tunable ifso desired. The variable condenser 8 is shown connected to theuni-control device 6 for variation therewith whereby the tuning means 3,5 and 8 may be simultaneously operated for selecting the desired carrierwave frequency.

At 9 there is shown a second amplifier, the conventional representationbeing understood to designate the same type of amplifier as designatedby the reference character 1, whereby further amplification of theseparated carrier wave may be secured. The carrier wave amplifiers 'Iand 9 are coupled by a piezo-electric coupling arrangement to insurecomplete separation of the carrier wave from its associated side bands.Thus, the piezo-electric arrangement comprises a quartz crystal I Eldisposed between the two pairs of metallic plates in a manner well knownto those skilled in the art. The crystal coupling will transmit a bandincluding cycles or less and therefore may be considered as insuring asubstantially complete separation of carrier wave and side bands.

Hence, the path including the amplifier 1, the coupling IU and theamplifier 9 may be considered as a carrier wave amplifier, and it is tobe clearly understood that the characteristics of these three elementsare so chosen that the carrier wave energy is amplified more than theside band energy, the amplifier 2 being employed primarily foramplifying the side band energy.

For controlling the gain of each amplifier 2,

'I and 9, it is ldesirable to include a volume control device in thecircuit of each of these amplifiers. Each volume control device may beconcircuit. Thus, variation of amplifier grid bias, cathode emission, orany other very well known type of gain control device may be employed.

In order to adapt the carrier wave amplifier band to different carrierwave frequencies, the crystal I0 is conventionally represented asvariable by an arrow, the arrow being shown connected, as at 8', to theuni-control tuning means 5 for simultaneous operation therewith.

It is not believed necessary to disclose herein the construction of avariable crystal coupling device, it being pointed out that any meanswell known in the prior art which is capable of replacing a crystal ofone definite frequency by a crystal of another definite frequency may beemployed. Such a variable piezo-electric arrangement is disclosed, forexample, by Trogner in 75 Cil U. S. Patent 1,727,575. Other variable,piezoelectric devices may be employed, it being understood that itisdesirable to have the piezo-electric coupling between the carrier waveamplifiers I and 9 adapted for adjustment to different carrier wavefrequencies simultaneously with the tuning devices 3, 5 and 8.

The amplified outputs of the amplifiers 9 and 2 are impressed upon theinput circuit of the detector 4, as at Il. The combined carrier wave andside band energy is then detected by any of the detection methodsdesired. Detected energy may then be directly utilized by head phones oraloud speaker, or the usual audio frequency amplifier, of one or morestages, may be disposed between the detector and the utilization means.When the receiving circuit shown in Fig. 1 is employed in a system forreducing interference between broadcast stations by transmitting sidebands at full amplitude and carrier at reduced amplitude, it isnecessary that interfering stations also transmit with reduced carrier.

Then, when the receiver is tuned to one station, other stations ondifferent frequencies may interfere by forcing their side band currentsinto Y the receiver, but the carriers of these interfering stations willbe very weak, and hence, the interfering side bands, beating with theirown carriers, will produce only a small amount of audio frequencycurrent in the detector. The interfering side bands will beat with thecarrier of the desired station, but the result of this will be currentsof very high audio frequency to which the audio amplifier and loudspeaker will not respond. The resulting interfering currents in the loudspeaker Will not be as troublesome as those received under presentconditions where the carrier is transmitted at full amplitude.

The reception method shown in Fig. 1 could also be utilized in areceiver in which the received carrier is augmented for the purpose ofgetting greatly improved fidelity of reproduction, and improvedselectivity, in addition to a reduction of the harmful effects ofselective fading, and possibly a slight reduction of staticdisturbances. It has been explained that the phenomenon termed selectivefading occurs mainly in the transmission and reception of short Waves.Thus, the energy is usually collected, at a point remote from thetransmitter, with the carrier Wave at subnormal amplitude, and the sidebands at normal amplitude. By regulating the amount of increase ofcarrier the reception method disclosed in Fig. 1 can be effectivelyemployed to amplify the carrier wave much more than the side bands so asto bring the carrier up to normal amplitude at the detector input. Theregulation of the increase of carrier will be treated more fully at alater point.

'I'he effective modulation degree of the received carrier wave may bereduced by the system shown in Fig. 1. It has already been explainedthat the amount of harmonics produced in the process of rectification ofmodulated signals depends on the degree of modulation of the carrierwave. Where a considerable amount of harmonics is produced, distortionresults. Thus, to reduce the amount of harmonic production in thedetector output, it is merely necessary to reduce the effective degreeof modulation of the carrier wave. This is accomplished in the systemshown in Fig. 1 by designing the amplifiers l and 9 in such a mannerwith respect to the amplier 2 that the carrier is amplified tosuper-normal amplitude. In other Words, in this utilization of thesystem shown in Fig. 1 the side bands and carrier wave are received atnormal amplitude.

It is desired to increase the amplitude of the carrier Wave with respectto the side band amplitude in order to reduce the effective degree ofmodulation of the carrier wave. Thus, it will be seen that the essentialdistinction between this use of the system and the previous two usesresides in the amplification of the carrier to supernormal amplitudefrom normal amplitude. However, it should be simultaneously observedthat all three utilizations of the reception method shown in Fig. 1involve the common method of separating the carrier wave from itsassociated side bands, amplifying the carrier wave independently of theside bands, and then combining both carrier wave and side bands fordetection and subsequent utilization.

It will be realized that the aforementioned third use of the presentreception method, that is amplification of carrier amplitude tosuper-normal amplitude for reducing detector output harmonics, may beemployed in conjunction with either of the first two uses.

For example, the amplifiers 'I and 9 may be so designed that a carrierwave, received at normal amplitude, will not only be amplified in orderto eliminate the effects of selective fading, but will be amplified tosuper-normal amplitude, with respect to side band amplitude, to reducethe effective degree of modulation of the carrier wave therebyminimizing the production of harmonics in the output of the detectorcircuit. Of course, the same treatment may be accorded a carrier wavewhich is deliberately transmitted at reduced amplitude in order toreduce interference between broadcast stations.

While Fig. l discloses the basic method of separating the carrier wavefrom its associated side band forindependent amplification, it will berealized that the method shown therein requires the use of a differentpiezo-electric crystal I for every carrier wave frequency desired. InFig. 2, there is illustrated a method of filtering a carrier frequencyout of a modulated wave in a more advantageous manner. A tunedmulti-stage radio frequency amplifier 2 receives the modulated carrierenergy from a source I through a coupling M. The tuning device 3 isshown as a suggested arrangement for selecting any desired carrier wavefrequency, the uni-control arrangement 6 being employed as in the caseof Fig. 1. The amplified carrier energy is impressed upon the input of afirst detector 4 through a coupling M1, the tuning condenser 5 beingemployed to select the carrier wave frequency; A local oscillator 4',including a tuning condenser 5', is arranged to impress voltage, as atM2, upon the input of the first detector 4.

The output circuit of the first detector, or frequency changing device4, includes the intermediate frequency energy. The intermediatefrequency current is now diverted into two separate paths. One of thesepaths includes an intermediate frequency amplifier Il, the input thereofbeing fixedly tuned to the desired intermediate frequency by the xedcondenser l 2, the input 0f the amplifier Il being coupled to' theoutput of the detector 4, as at M3. The amplifier l l may include, as iswell known to those skilled in the art, one or more stages ofamplification, and its output is coupled, as at M4, to the input circuitof a second detector, or frequency changing device l3, whose inputcircuit is fixedly tuned to the intermediate frequency by a fixedcondenser I2',

The second path through which the intermediate frequency current isdiverted includes an intermediate frequency amplifier I4 having itsinput circuit iixedly tuned to the intermediate frequency by a fixedcondenser I5, the input circuit of the amplifier I4 being coupled, as atM5, to the output circuit of the detector 4. A second amplifier I4',similar to the amplifier I4, has its input circuit coupled to the outputcircuit of the amplifier I4 through a piezo-electric crystal ID. Thiscoupling is accomplished in any manner well known to those skilled inthe art, the particular type of coupling shown herein involving the Wellknown device of disposing the crystal between two pairs of metallicplates, each pair of plates being connected to a particular amplifiercircuit. The amplified output of the amplifier I4 is impressed upon theinput circuit of the second detector I3 through a coupling M5. Energyfrom the local oscillator 4' is likewise impressed upon the inputcircuit of the detector I3 through a coupling Mfr.

The operation of the system shown in Fig. 2 will now be explained up tothe detector I3, as a clear understanding of the reception methoddepends upon a clear appreciation of the action of the second detectorI3. It has been pointed out that the intermediate frequency currentexisting in the output circuit of the first detector 4 is transmittedthrough a second path including a piezo-electric element I0. In passingthe intermediate frequency current through the second path, such currentis in effect passed through a Very selective circuit, highly selectiveby virtue of the utilization of the quartz crystal I0 as the frequencyselecting element, which transmits the carrier but not the side bands.

The amplified unmodulated carrier is impressed through the coupling Msupon the second detector I3 simultaneously with heterodyne Voltage,obtained from the local oscillator 4', which was utilized in connectionwith the first detector 4 to obtain the intermediate frequency energy.Thus, it is possible` to restore, through the action of the secondfrequency changing device I3, the carrier wave to its original receivedfrequency.

For example, if the oscillator 4 is assumed to produce heterodynevoltage at 900,000 cycles, and the received carrier frequency is assumedto have a value of 1,000,000 cycles, while a certain side band has avalue of 1,001,000 cycles, it will be obvious that the intermediatefrequency energy produced in the output circuit of the detector 4 willinclude a frequency of 100,000 cycles, corresponding to the carrierfrequency, and a frequency of 101,000 cycles corresponding to the sideband. The amplifier II is designed to amplify intermediate frequencyenergy, including both the carrier wave and side band, in the usualfashion. On the other hand, the crystal I0 is chosen so as to pass onlythe 100,000 cycle energy corresponding to the carrier wave. Furthermore,the ampliers I4 and I4 are so chosen with respect to the amplifier IIthat energy of 100,000 cycles is amplified to a greater extent than theenergy amplified by the amplifier II.

It will now be seen that there is impressed upon the input circuit ofthe second detector I3 the 100,000 cycle energy from the carrier Waveamplifier, 900,000 cycleenergy from the oscillator 4', and amplifiedintermediate frequency current from the amplifier II. Thus, by tuningthe output circuit of the detector I3, after including a tuningcondenser I 6 therein, to the sum frequency of the 900,000 cycle energyand the 100,000 cycle carrier wave energy, there is obtained in theoutput circuit of the second detector the original carrier frequency of1,000,000 cycles. The tuned output of the detector I3 is designed so asto select the sum frequency, and reject the difference frequency and theother frequencies present in the output circuit of the second detectorI3.

Obviously, the original side band frequency of 1,001,000 cycles willalso be present in the tuned output circuit of the second detector. Itis now only necessary to couple a third detector I8, having its inputcircuit tuned by a condenser II, to the output of the second detectorI3, as at M8, in order to detect the carrier and side band energy. Thedetected output of the detector I8 may then be amplified at audiofrequency in any well known manner and subsequently utilized by headphones, a loud speaker, or in any other similar manner.

-The tuning devices 3, 5 and 5', I6 and I'I are all shown arranged formechanical uni-control by the element 6, it being obvious that suchunicontrol operation may be varied depending upon the variations of thebasic method disclosed in Fig. 2.

While it may appear that the arrangement shown in Fig. 2 involves acertain degree of complexity in separating the carrier wave from itsside bands, with respect to the method shown in Fig. l, it is pointedout that it is much easier to accomplish the filtering of the carrierwave from side bands at a relatively low frequency, such as at or 200kilocycles, than at a higher frequency, since circuits are much moreselective at low frequencies.

Additionally, the arrangement shown in Fig. 2I permits the use of aquartz crystal which is the most selective circuit that can be obtained.Instead of tuning the selective circuit to the carrier frequency, whichis either impossible since the resonant frequency of a quartz crystalcannot be changed, or highly complicated as a -series of differentquartz crystals are to be used, the frequency of the received signal ischanged to agree with the frequency of the selecting circuit.

Thus, it will be realized that the method shown ,in Fig. 2 offers asimple and practicable method of accomplishing a result which can beobtained only with great diiiiculty by other methods. It is intended tobe used in a receiver, in which the received carrier is amplied fromsub-normal arnplitude (caused by selective fading phenomena or bydeliberate transmission of carrier at reduced amplitude to minimizeinterference between broadcast stations) for the purpose of gettinggreatly improved fidelity of reproduction, and improved selectivity, inaddition to a reduction of the harmful effects of selective fading, andpossibly a slight reduction of static disturbances. It is likewisepointed out that the method shown in Fig. 2 can be employed for reducingthe production of the second harmonic in the output of detector I3 by sodesigning the amplifiers I4 and I4' with respect to the amplifier IIthat the carrier wave amplitude is increased to super-normal amplitude,thereby reducing the effective degree of modulation of the carrier wave.

The manner of dealing with selective carrier fading, and general carrierfading, will now be 'considered in detail.

this channel so that when the received carrier is strong, the carrieroutput from the carrier channel is weak, and vice versa, and then addthis extra carrier to the currents (including carrier) in the otherchannel. If the carrier channel is working right, then the sum of thecarrier output of the signal channel and the output of the carrierchannel will 'be constant. This sum energy is then impressed on thedetector.

The other method is to amplify the carrier to a high level in a separatechannel, possibly using a limiter to keep the carrier from exceeding acertain maximum value. This extra carrier is then added to the signaloutput of the signal channel, and impressed on a linear detector. Alinear detector has the property that if the carrier is much larger thanthe side bands, the carrier amplitude may vary without changing theoutput.

If the carrier varies, the output of the linear detector remainsconstant. Therefore if the carrier is made large enough, it can varyconsiderably (fade) and yet cause no trouble.

Another method of signal correction is to be distinguished from theabove two methods, as itA does not correct for selective fading thoughit would probably reduce the bad distortion occurring when the carrierfades out too much, but only for general fading of the whole frequencyband.

In this scheme, when the signal fades, the extra carrier channel injectsmore carrier into the signal channel just ahead of the second detector(Which must be a square-law detector) so that the carrier at thedetector grid increases when the signal fades, and vice versa. Thus,when the signal is weak, the extra carrier shifts operation to thesteepest part of the detector curve, Where the detector is relativelyefficient, and when the signal is strong the extra carrier is reduced somuch that the total carrier is less than' before, and detection occursat a point on the characteristic where the eiiiciency is lower so thatthe larger side bands produce only as much audio output as before.

In Fig. 3 there is shown an embodiment of the present inventionparticularly adapted for use in a system requiring correction for signalfading. Assume that the source I collects modulated carrier energy withthe carrier at a subnormal amplitude because of fading phenomena. Thecollected energy is fed into a radio frequency amplier 2' comprising oneor more stages of tuned radio frequency amplification, through acoupling Mi. The amplified output of the amplifier 2 is then divertedinto two paths, one of which paths comprises a second radio frequencyamplifier 3', Whose input is coupled as at M2, to the output of theamplifier 2'. The output of amplifier 3 is coupled, as at Ms, to thedetector, or demodulator Il, the latter having a square lawcharacteristic.

The second path into which the amplified currents of the amplifier 2 arediverted comprises an amplifier 5' having a tuned input circuit coupled,as at M4, to the output circuit of the amplifier 2'. A carrier frequencyoscillator 1' has its input circuit coupled, as at M5, to the output ofthe amplifier 5', the output of the oscillator being coupled to theinput of the demodulator tube 4'.

Tuning condensers are conventionally shown disposed in each of the inputcircuits of the ampliers 2', 3', 5', the demodulator 4' and the carrierfrequency oscillator 1', all the condensers being shown as arranged, formechanical unicontrol, as at 6. The output of the demodulator 4' may beimpressed upon an audio amplifier and subsequently utilized in anydesired fashion.

The operation of the arrangement shown in Fig. 3 has been explainedheretofore. The collected modulated carrier energy is diverted into twochannels after amplification at 2. The first channel amplifies the radiofrequency and feeds into the demodulator 4'. The demodulator l4'Acomprises the square law second detector already referred to.

It Will be noted that the screen grid tube V1 functions as a detectorwhose input electrodes are connected across the output of amplifier 5'.Bias for the grid of amplifier tube V3 is secured across the resistorR2. This bias increases With increase of detector (V1) swing, thusreducing the amplification of V3, and the amount of energy fromoscillator l fed into the demodulator input 4 through coupling M9. Thedemodulator 4' operates along a square law characteristic, and as thetotal energy goes down, the carrier increases, thus suppressing fading.

While I have indicated and described several systems for carrying myinvention into effect, it will be apparent to one skilled in the artthat my invention is by no means limited to the particular organizationsshown and described, but that many modifications may be made withoutdeparting from the scope of my invention as set forth in the appendedclaims.

What I claim is:

1. A method of reception which consists in collecting modulated carrierenergy, producing local oscillations, combining the collected energy andthe local oscillations to produce intermediate frequency energy,separating the carrier of the intermediate frequency energy from itsassociated side bands, amplifying the separated carrier to a greaterextent than the side bands, combining the amplified carrier and saidside bands, selecting the sum frequencies of said last mentionedcombined energy and detecting the Selected sum frequency energy.

2. The method of overcoming selective fading due to a phase shift of thecarrier with respect to the side bands in a carrier system in which thetransmitted carrier is set out at a lower value than the side bandamplitude, which consists inV collecting at the receiver the transmittedenergy, separating the carrier wave from its associated side bands,amplifying the separated carried Wave independently of the side bands toa value equal to that of the side band amplitude without affecting theside bands, combining the amplified carrier wave and side bands anddetecting the combined energy.

3. The method of overcoming selective fading due to a phase shift of thecarrier with respect to the side bands in a carrier system in which thetransmitted carrier is sent out at a different value than the side bandamplitude, which consists in collecting at the receiver the transmittedenergy, separating the carrier wave from its associated side bands,amplifying the separated carrier Wave independently of the side bands toa value higher than that of the side band amplitude, combining theamplified carrier wave and side bands and detecting the combined energy.

4. The method of overcoming selective fading due to a phase shift of thecarrier with respect to the side bands in a carrier system in Which thetransmitted carrier is sent out at a lower value than the side bandamplitude, which consists in collecting at the receiver the transmittedenergy, separating the carrier wave from its associated side bands,amplifying the separated carrier wave independently of the side bands toa value higher than that of the side band amplitude, combining theamplified carrier Wave and side bands and detecting the combined energy.

5. In a carrier current system for overcoming selective fading in whichthe carrier is transmitted at a subnormal amplitude, the method ofreception which consists in collecting signal energy, filtering thecarrier wave from its associated side band, amplifying the filteredcarrier wave to a greater extent than the side bands to raise thecarrier to normal amplitude so as to maintain a predeterminedrelationship between the carrier and the side band amplitudes, combiningthe amplified carrier and side bands and detecting the combined energy.

6. The method of overcoming selective fading due to a phase shift of thecarrier with respect to the side bands in a carrier system in which thetransmitted carrier is sent out at a different amplitude than the sideband amplitude, which consists in collecting at the receiver thetransmitted energy, separating the carrier wave and side bands at arelatively low radio frequency, amplifying the separated carrier andside bands independently, obtaining a greater amplification of thecarrier than the side bands, and subsequently combining the carrier waveand side bands, both at substantially the same amplitude.

7. In a carrier system for overcoming selective fading wherein a carrierand sidebands are transmitted, a receiver comprising an energycollector, a radio frequency amplification path arranged to amplify thecollected energy coupled to said collector, a tuned circuit in saidpath, a second amplifying path connected to said energy collector, and atuned circuit connected in said second path, a piezo-electric filteringmeans in said second path for discriminating against frequencies otherthan said carrier frequency, said second path being arranged to amplifysaid carrier wave to a predetermined value at least equal to that ofsaid side bands, output circuits for said two paths, and a detectorcoupled to said output circuits, a tuned circuit associated with saiddetector, and unicontrol means mechanically linked with all three ofsaid tuned circuits.

8. In a carrier system for overcoming selective fading wherein a carrierand sidebands are transmitted, a receiver comprising an energycollector, an amplifier for amplifying the received energy, a firstdetector coupled to said amplifier, and a local oscillator coupled tosaid first detector for producing an intermediate frequency, a seconddetector having input and output circuits, an intermediate frequencyamplifier coupling the input energy amplifier,

of said second detector with the outputv of said first detector, and asecond intermediate frequency amplifier for amplifying the intermediatecarrier frequency to an extent greater than that aorded said side bandsby said first intermediate frequency amplifier, and coupling coils forcoupling both said local oscillator and the output of said secondintermediate frequency amplifier with the input of said second detector,and means in circuit with the output of said second detector forobtaining the sum frequencies of said local oscillator and theintermediate carrier frequency.

9. In a radio receiver, a modulated carrier a detector circuit, a pathextending from the output of said amplifier to the input of saiddetector arranged to pass both the carrier and its associated sidebands,and means including an oscillator in circuit with said path tuned to thecarrier for amplifying the carrier independently of the sidebands.

l0. A method of reception which includes the steps of collecting signalmodulated carrier energy, producing local oscillations of the samefrequency as the collected carrier energy, controlling the amplitude ofthe generated oscillations in accordance with the intensity of thecollected carrier energy, controlling the phase of the generatedoscillations in accordance with the collected car. rier energy andcombining at least a portion of the generated oscillations with thecollected modulated carrier energy in such a way that the resultantproduct energy comprises modulated carrier energy, the carrier componentof which is of approximately constant amplitude and of proper phaserelationship with respect to its as sociated side bands, and derivingthe desired signals from the resultant product energy.

l1. A method of reception which includes the steps of collectingmodulated carrier energy, producing local oscillations, combining thecollected energy with a portion of the locally produced oscillations toproduce intermediate frequency energy,separatingthe carrier of theintermediate frequency energy from its associated side-bands, amplifyingthe separated carrier and the side-bands, the separated carrier beingamplified to a greater extent than the side-bands, combining the ampliedcarrier, the amplified side-bands and another portion of the locallyproduced oscillations, selecting from said combination the sum frequencyof the frequency of the amplified carrier and the frequency of thelocally produced oscillations, detecting the selected sum frequencyenergy and utilizing the detected energy to produce the desired signals.

RENE A. BRADEN.

